Highlighting not working

[Grestorn]

I'm using a simple dfs query with es but for some reason the highlighting doesn't work. What am I doing wrong?

Here's an except the Domain that's searched:

class Story {

    static searchable = {
        only = ['author', 'creationDate', 'publishDate', 'owners', 'id', 'name', 'summary', 'text', 'category']

        author reference:true
        owners reference:true
        category reference:true

        root true
    }
   ...

This is the search call and the highlight settings:

        def highlighter = {
            field 'text'
            field 'summary'
            field 'author.name'
            preTags '<mark>'
            postTags '</mark>'
        }

            def txtSrchResult = Story.search(searchType: 'dfs_query_and_fetch', highlight: highlighter, from: params.offset, size: params.max, sort: params.sort, order: params.order) {
                bool {
                    if(searchTerm?.length() > 0) {
                        must {
                            query_string(query: searchTerm)
                        }
                    }
                    if(! isAdmin) {
                        must {
                            term(deleted: false)
                        }
                        must {
                            term(previouslyApproved: true)
                        }
                    }
                    if(checkids != null) {
                        must {
                            ids(values: checkids)
                        }
                    }
                }
            }

The search itself works fine, I get the results I'm looking for. The "highlight" list is also returned, but it doesn't contain any fragments whatsoever. None of the fields is ever present in the maps, even though the hit is definitely in the text and/or summary.

What am I missing here?